The present invention generally relates to fuel injectors, and more particularly high pressure gaseous fuel injectors for internal combustion engines.
The natural gas transmission industry and chemical process industries use a large number of large-bore, 2-stroke and 4-stroke natural gas engines for compressing natural gas. For example, industries use these engines for such purposes as maintaining pressure in the extensive network of natural gas pipelines that supply residential housing and commercial businesses. The network of natural gas pipelines typically operate at high pressures in the neighborhood of between 500 psig and 1000 psig.
These large-bore, natural gas engines may be powered by a small portion of the natural gas passing through the pipelines. However, before being injected into the engine, the pressure of the gas is significantly and substantially reduced. Gaseous fuel is typically injected into these cylinders at low pressures (for example, 15 psig to 60 psig by mechanically actuated fuel injectors, such as that disclosed in Fisher, U.S. Pat. No. 4,365,756. The problem with low pressure injection is that the fuel pressure provides little kinetic energy with which to induce cylinder charge mixing. There is ample evidence that the fuel and air in these large bore engines are not well mixed and as such exhibit poor combustion stability, high misfire rates and significant cycle-to-cycle variations in peak pressure. As a result, these engines are not efficient and also are environmentally detrimental, contributing to approximately 10% of the total NOx production in the United States from stationary combustion sources according to estimates.
The concept of using high pressure fuel delivery to enhance fuel mixing in these engines has been proposed as a means to improve efficiency and environmental emissions from these engines. However, retrofitting existing engines provides a significant hurdle because these engines are manufactured by different companies and also vary in size. Moreover, injecting fuel at high pressure as opposed to low pressure requires the fuel injectors to operate under extremely high operating pressures which in turn greatly increases stresses and powering requirements for opening and closing the valves. A key requirement for any proposed high pressure fuel injector is reliability. These large-bore, natural gas engines typically run continuously over long time periods, meaning that any suitable fuel injector must be capable of reliably enduring very long operating cycles of the engine. It is desirable for example, that the fuel injectors reliably operate over several hundred million continuous cycles of the engine (about one to two years before replacement). As such, a valve must achieve reliability over this long time period or operating interval. Fuel injectors of the prior art such as that disclosed in Fisher, U.S. Pat. No. 4,365,756 are not capable of reliably sealing and accurately controlling the injection of gas at high pressure. Only recently have economic and environmental pressures on the gas industry resulted in justification for advances in fuel injection technology. For at least the foregoing reasons, commercial large bore 2-stroke and 4-stroke natural gas engines continue to be fueled at low pressure by conventional low pressure fuel injectors.
It is the general aim of the present invention to provide a commercially reliable and practical fuel injector for injecting high pressure gaseous fuel (eg. around 300-700 psi or more) into combustion engines.
It is an object of the present invention according to one aspect to provide a fuel injector that can withstand the forces of high pressure gaseous fuel and has a long service operation but does not leak either gaseous fuel or hydraulic fluid to the external environment.
It is another object of the present invention according to another aspect to provide a fuel injector that is universal in that the fuel injector assembly can be easily adapted without any or any substantial redesign to fit and operate as desired on the various types and sizes of combustion engines in industry.
It is a another object of the present invention according to another aspect to provide a highly reliable fuel injector, and specifically one that is not susceptible to thermal damage from the engine.
It is another object to provide a fuel injector with increased operating life, whereby gas leakage, eventually expected from o-rings and sliding gas seals, is captured and safely and properly disposed of, on an ongoing basis, not requiring engine shut-down to replace the injector valve.
In accordance with these and other objectives, the present invention provides a fuel injector cartridge and a fuel injector incorporating the same, that uses the relatively cool gaseous fuel passing through the valve to directly cool the exposed surface of the valve and therefore limit the amount of heat transferred from the engine cylinder to the gas seals. The fuel injector cartridge includes a valve body having an outer sleeve, and upper and lower guide collars mounted in the sleeve. The stem of an elongate valve extends up into and through the guide collars for radial retention. The valve is slidable through the guide collars for linear reciprocating movement between open and closed positions. The guide collars are separated by a cooling chamber (which in the preferred embodiment doubles as a spring chamber) in which a portion of the valve stem is exposed. The sleeve has at least one cooling port (that takes the preferred form of a plurality of cross-holes) that allows the cool gaseous fuel to pulsate into and out of the cooling chamber correspondingly as the valve opens and closes. During opening of the valve, gas pressure drops in the gas passageway, resulting in a suction effect sucking the now heated gas (by virtue of direct contact with the valve, spring and guides) out of the cooling chamber. During closing of the valve, the pressure increases in the gas passageway forcing new more cool gaseous fuel into the cooling chamber.
It is an aspect of the present invention that the lower collar guide is a self lubricated high temperature graphite/carbon bushing. A bushing retainer is provided below the bushing to prevent any chips which may form from dropping into the outlet port.
It is another aspect of the present invention that a metal O-ring is used at the between the bottom of the cartridge and the cartridge housing to provide a seal axially between the cartridge housing and the cartridge body. The metal O-ring can withstand the high temperatures nearest to the cylinders of the engine and provide a highly reliably seal at the same time. Means in the preferred form of load washers engage the other axial end of the valve housing to axially compress the metal O-ring. A force in the rough neighborhood of about 10,000 is necessary to maintain a seal for high pressure fuel injection over about 300 psi.